[JoaoSilva]

Hello everyone,

I am trying to simulate the wind flow over a terrain where I need to define the turbulent viscosity via UDF as function of height above the ground.
The problem is that the following UDF give the absolute coordinate z (over the plan z=0) rather than local coordinate (over the ground surface):

#include "udf.h"
#define L -86
#define Ustar 0.4

DEFINE_TURBULENT_VISCOSITY(user_mu_t,c,t)
{
real x[ND_ND];
real mu_t, z;
C_CENTROID(x,c,t);
z=x[2];
mu_t=0.41*Ustar*z/pow((1-16*z/L),-0.25);
return mu_t;
}

I don't know how I can get the height of the terrain (h) for each iteration at the same x and y position that a given cell centroid along the domain given by C_CENTROID(x,c,t). With that I would intend subtract h from z to get the local coordinate z.
This could not the unique way to get local coordinate z, but I don't know another one.

I would appreciate any suggestion to solve this problem.